An ionomer such as Surlyn® which is readily available commercially from E. I. du Pont de Nemours and Company, Wilmington, Del., USA (DuPont), has been used in packaging applications for many years for its heat seal properties and toughness in flexible packaging. It is used in cosmetics packaging for aesthetics such as perfume caps, bottles, or cases. An ionomer is also used to replace PVC in flooring. Ionomers are generally produced by neutralization of ethylene acid copolymers with zinc or sodium metal ions. Such ionomers may have a tendency to pick-up a static charge, more so than alternative materials such as polyethylene. The static charge attracts dust, negatively affecting the appearance of cosmetics packaging and causing contamination of the seal area in flexible packaging thereby affecting the use of such ionomers in the packaging of powdered foods (such as cake mixes, powdered drinks, and shredded cheese) due to the static nature of Surlyn®. Dust accumulation can detract from the appearance of the packages. By reducing the tendency of an ionomer to attract dust, one can grow the use of ionomer in packaging market.
Surface resistivities (for electric current flowing across a surface as the ratio of the DC voltage drop per unit length to the surface current per unit length) covering the range from highly conductive materials to insulators include highly conductive: 10−6 to 10 Ohms/square; conductive: 102 to 104 Ohms/sq; dissipative: 104 to 1011 Ohms/sq; and insulating: 1011 to 1016 Ohms/sq.
Ionomers made with potassium ions exhibit antistatic properties for they reduce the surface resistivity and static decay times of the polymer so that they may be suited for demanding applications such as the packaging of electronic components.
Antistatic resins, such as a highly neutralized potassium ionomers MK400, available from DuPont-Mitsui (MDP), Tokyo, Japan, have surface resistivities of about 108 to 1011 Ohms/sq. Antistatic resins may have poor mechanical properties, poor thermal instabilities, etc. For example, highly neutralized potassium ionomers may be susceptible to moisture pick-up, which affects its physical properties. In potassium neutralized ionomers, very high levels of potassium ions (as high as 70% neutralized) are needed to achieve such properties.
It is therefore desirable to develop a new ionomer composition that does not require such high potassium neutralization but capable of reducing the ionomer's tendency to build up charges.